In optical disk drives the first action after inserting a disk is disk recognition. Disk recognition is used to determine to which disk family the inserted disk belongs and to determine the specific disk type within the family. Disk families are Compact Disk (CD) with a 1.2 mm substrate, Digital Versatile Disk (DVD) and High-Definition DVD (HDDVD) with a 0.6 mm substrates and Blu-Ray disk (BD) with a 0.1 mm cover layer through which the disk is readout. Each family is associated with a variety of standards for a plurality of disk types, associated with e.g. the physical and logical format of the disks, and with operating conditions, such as the laser wavelength and numerical aperture (NA) of the objective lens with which the disk can be read and/or write the disk, and e.g. the tracking method associated with the disk type. The standards for CD specify a NA of 0.45-0.52 and an infrared laser (with a wavelength of typically 780 nm), the standards for DVD specify a NA of 0.60 and a red laser (630-690 nm), the standards for HDDVD specify a NA of 0.67 and a blue laser (typically 405 nm) and the BD standards specify a NA of 0.85 and also a blue laser (typically 405 nm).
The plurality of disk types within a family typically include one or more read-only types (ROM) associated with a track comprising embossed pits, one or more one-time recordable types (R) associated with one-time writable, generally non-erasable, marks in a recording material, e.g. a dye layer, in an empty track and one or more re-recordable or rewritable (RE, RW, RAM) types associated with writable and erasable marks in typically a phase-change material in an empty track. E.g., the CD family comprises CD-ROM (including CD-Audio), CD-R and CD-RW, the DVD-family comprises DVD-ROM, DVD+R, DVD-R, DVD+RW, DVD-RW, DVD-RAM, DVD-R-QFlix (a different type of DVD-R disks), the HDDVD-family comprises HDDVD-ROM, HDDVD-R, HDDVD-RW, HDDVD-RAM and the BD-family comprises BD-ROM, BD-R and BD-RE. One may note that especially for the 0.6 mm family quite a large amount of disk types exists. On top of the listed types, many disk types also exist in dual layer (and even triple layer) derivates which must also be recognized.
In general, a recordable (like R/RW/RAM types) disk has a low reflection and contains a wobbled groove. The groove generates the Push Pull (PP) tracking signal from the empty disk (as well as from recorded parts), while the high frequent wobble is decoded with addressing information. The recorded part of the recordable disk might in some cases also generate a Differential Phase Detection (DPD) tracking signal from the recorded marks. In general, a ROM disk has high reflection and only contains a spiral of embossed pits. Beside a DPD tracking signal, sometimes also a Push Pull signal is generated. It is therefore not an easy task to reliably determine the disk type by current methods based on reflection and DPD signal level.
In prior art optical drives the tracking method is determined by selecting one of the two tracking methods prior to the situation where the actual disk type has been positively identified. If the chosen tracking method results in a “tracking ok”, the system is in radial tracking mode and the system can try to read out data from the wobble. If it is possible to read out data, the inserted disk is assumed to be a recordable one, the PP tracking method has to be chosen for further operation of the disk. If the selected one was DPD the system needs to switch to PP. Each time the tracking method changes, the new tracking mode has to be initialised. To read the wobble data, also the correct wobble path has to be initialised. This trial-end-error method is not always robust enough and retries are necessary.
For some disk types, the disk is prepared with a disk recognition area allowing to recognize e.g. a blue-laser family disk with a red-laser. E.g., for HDDVD disks a so-called system lead-in area is specified at the inner disk zone. Though this area is readable by red laser, it may be hard to locate this area in a low-cost drive without accurate sledge control, as the system lead-in area is a very narrow band which may be hard to find. Especially when a drive design is used without a calibrated radial home position, it can not be guaranteed that an attempted jump into the system lead-in area for HDDVD actually reaches that area. When attempting to recognize a HDDVD disk, prior art optical disk drives thus generally use a trial-and-error method attempting to read the disk with the red laser and the blue laser in turn, and recognizing the disk with one of the lasers.